Method for operating an exhaust valve for diesel particulate filter regeneration

ABSTRACT

A method of operating an exhaust valve ( 28 ) to heat a diesel oxidation catalyst ( 23 ) and to initiate regeneration of a DPF ( 24 ) includes the steps of determining whether the DPF is being cleaned, and determining the speed and quantity of fuel injected into the engine. The method also includes determining an engine back-pressure set point based on whether the engine  14  is fueling. If fueling, the set point is based on the quantity of fuel and the engine speed. If not fueling, the set point is based on whether there is an other request for actuation of the exhaust valve ( 28 ). An exhaust valve set point is determined based on the engine back pressure set point and a current engine back pressure. The exhaust valve ( 28 ) is actuated in response to the exhaust valve set point to obstruct the flow of exhaust gas, where the exhaust gas is heated and initiates regeneration of the DPF ( 24 ).

BACKGROUND

Embodiments described herein relate to a system and method for regenerating a diesel particulate filter of an exhaust gas aftertreatment system. More specifically, embodiments described herein relate to a system and method for regenerating a diesel particulate filter of an exhaust gas aftertreatment system using an exhaust valve.

Exhaust gas aftertreatment systems in diesel vehicles are located downstream of an engine for treating exhaust gases emitted from the engine. The aftertreatment systems typically include a diesel oxidation catalyst, and a diesel particulate filter, among other components. An exhaust valve is a valve that opens and closes the exhaust duct to selectively permit the flow of exhaust gas through the exhaust system to an ambient. Typically, the exhaust valve is actuated or closed only during engine braking to create a backpressure in the engine, and for cold ambient warm-up.

Particulate matter from the exhaust gas accumulates on the diesel particulate filter, and if left unchecked, can create a back pressure in the aftertreatment system. A regeneration event is the periodic oxidation of the collected particulate matter in the aftertreatment system during routine diesel engine operation. When the diesel particulate filter of the exhaust system experiences a build-up of particulate matter, the particulate matter is oxidized to “regenerate” the filter. Regeneration is typically initiated by increasing engine load and activating a post-injection of diesel fuel into the exhaust stream. This post-injection provides sufficient heat to oxidize the trapped particulate matter within the aftertreatment system.

To provide the exhaust gas with enough thermal energy to conduct sufficient heat to the diesel particulate filter to initiate regeneration, the loading of the engine is typically increased. However, many vehicles run on a “stop and drive” basis, where the engine is typically run at a low speed and low loading. During low speed and low load operation of the engine, the resulting exhaust gas may not have a sufficiently high temperature to initiate the regeneration.

SUMMARY

A method of operating an exhaust valve to heat a diesel oxidation catalyst to initiate regeneration of a diesel particulate filter on an exhaust aftertreatment system associated with an engine includes the steps of determining whether the diesel particulate filter is being cleaned, and determining the speed and quantity of fuel injected into the engine. The method also includes determining an engine back pressure set point based on whether the engine is fueling. If the engine is fueling, the engine back pressure set point is based on the quantity of fuel and the speed of the engine. If the engine is not fueling, the engine back pressure set point is based on whether there is an other request for actuation of the exhaust valve. The method also includes the steps of determining a current engine back pressure, and determining an exhaust valve set point based on the engine back pressure set point and the current engine back pressure. The exhaust valve is actuated in response to the exhaust valve set point to at least partially obstruct the flow of exhaust gas through a fluid passageway of the exhaust aftertreatment system, where the exhaust gas is heated in the fluid passageway and initiates regeneration of the diesel particulate filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an exhaust aftertreatment system having a diesel particular filter located downstream of an engine.

FIG. 2 is a flow diagram showing the method to operate the exhaust valve shown in FIG. 1; and

FIG. 3 is a flow diagram showing the method to operate the exhaust valve continued from FIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 1, an exhaust gas aftertreatment system is indicated generally at 10, and has an exhaust pipe assembly 12 extending from an engine 14 to an outlet 16, such as the outlet to an ambient 18. The exhaust pipe assembly 12 forms a fluid passageway 20 for the flow of exhaust gas F from the engine 14 to the ambient 18.

A first portion 22 of the exhaust pipe assembly 12 extends from the engine 14 to a diesel oxidation catalyst (DOC) 23. Downstream of the DOC 23 is a diesel particulate filter (DPF) 24. The DPF 24 is a filter constructed from a very high temperature resistant material. The DPF 24 catches and holds particulate matter entrained within the exhaust gases discharged into the exhaust aftertreatment system 10. The DPF 24 is periodically regenerated to limit increases in exhaust aftertreatment system 10 back pressure and to maintain engine 14 efficiency. A second portion 26 of the exhaust pipe 12 assembly extends from the DPF 24 to the outlet 16. Other components may be disposed on the on the aftertreatment system 10. Although the exhaust pipe assembly 12 is shown in three separate portions, other numbers and configurations of exhaust pipe assembly are possible.

An exhaust valve 28 is located upstream of the DOC 23 on the fluid passageway 20. The exhaust valve 28 is actuated with an exhaust valve controller 30 to increase the temperature at the DOC 23, which initiates regeneration at the DPF 24. When actuated, the exhaust valve 28 obstructs the flow of exhaust gas F through the fluid passageway 20. When the exhaust valve 28 closes, partially or completely, the exhaust gas F in the aftertreatment system 10 upstream of the exhaust valve 28 is compressed, resulting in an increase in temperature of the exhaust gas F. Also, the resistance to pistons in the engine requires a greater amount of fuel injection in the cylinders to meet the engine set point. A diesel injection, in combination with the operation of the exhaust valve 28, creates additional heat energy in the exhaust gas F to heat the DOC 23. The increased temperature of exhaust gas F upstream of the exhaust throttle valve 28 is transferred to the DOC 23 and to the DPF 24 as the exhaust gas flows downstream to the DPF. The heated exhaust gas F provides sufficient heat to initiate regeneration (soot oxidation) at the DPF 24.

A sensor 32 senses and communicates at least one of many variables to the engine control module 36 of the engine with a sensor controller 34. The sensor 32 may sense the backpressure in the aftertreatment system 10 and/or the temperature in the aftertreatment system so that the engine control module 36 can determine whether the DPF 24 is ready to be regenerated. Further, the sensor 32 may sense the acceleration a, speed s, fuel injection quantity q, and braking torque t, at the engine 14, as will be discussed below with respect to FIGS. 2 and 3. It is possible that the sensor 32 comprises more than one sensor that communicates multiple variables to the engine control module 36. It is also possible that sensor controller 34 may output one or more values to another controller other than the engine control module 36. Further, the controllers 30, 34, 36, 38 can be implemented into the system in various ways, such as a single controller for one or more components, or multiple controllers for each component.

An engine brake controller 38 communicates to the engine control module 36 whether an engine brake 40 is being used. In response to the values sensed by the sensor 32 and communicated by the sensor controller 34, and the values communicated by the engine brake controller 38 from the engine brake 40, the engine control module 18 actuates the exhaust valve 28 through the exhaust valve controller 30, which selectively opens and closes the passageway 20 from the engine 14 to the ambient 18.

Referring to FIGS. 2 and 3, the method for operating the exhaust valve 28 is indicated generally at 100 and is implemented in the engine control module 18. Although the following description will be with respect to the method of FIGS. 2 and 3, it is possible that the method can be implemented in numerous ways and with a different number and order of steps.

The method starts at start step 102 by determining whether the DPF 24 is being cleaned at determination step 104, and if not, the method loops back to the start step 102. The engine control module 36 includes the software to execute the method of FIGS. 2 and 3, however it is possible that a separate controller can be used.

If the DPF 24 is being cleaned, for example as determined by the engine control module 36 based on the sensor 32 and communicated by the sensor controller 34, an acceleration a of the accelerator pedal is determined at acceleration determination step 106, and an engine speed s is determined at engine speed determination step 108. Using the acceleration value a, it is then determined whether the engine is receiving fuel, or whether the engine is not receiving fuel at acceleration value step 110. Specifically, it is determined whether acceleration value a is greater than zero at step 110, where a greater than zero result would imply that the engine is fueling, and where a not greater than zero result implies that the engine is not fueling.

If the engine is fueling, a fuel quantity q is determined at fuel quantity step 112. Using the fuel quantity q and the engine speed s, an engine back pressure set point x1 is set at set point step 114. There are multiple ways of determining the engine back pressure set point x1. One example of determining the engine back pressure set point x1 is by using one or more predefined look up tables (not shown) using the fuel quality q. Another example of determining the engine back pressure set point x1 is to calculate the determined engine back pressure set point x1 using well known mathematical formulas. Yet another example of determining the engine back pressure set point x1 is to find an average or a mean of multiple fuel quality values.

Continuing with FIG. 2, if the engine 14 is not fueling at step 110, it is then determined whether there is another request for the exhaust valve 28 at other request determination step 116. These requests may come from multiple components that may want to control the exhaust valve 28. If a request for use of the exhaust valve 28 is made at step 116, the determined engine back pressure set point x1 would be set based on this other request at an other request set point step 118. The determined engine back pressure x1 can be set in a number of ways, as is known in the art.

One of these other requests may be from the engine brake controller 38 when the engine brake 20 is being used. The engine back pressure set point x1 is then generated based values from the engine brake controller 22, which is outputted to the engine control module 36.

If there is no other request at step 116, a braking torque t is determined at brake torque determination step 120, and is used with the engine speed s in setting the determined engine back pressure set point x1 at brake torque set point step 122.

Once the determined engine back pressure set point x1 has been determined at steps 114, 118, or 122, a correction value c may also be determined at correction step 124. A current engine back pressure x2, which indicates the state of the current engine back pressure, is determined at current back pressure determination step 126. The correction value c makes adjustments to correct the engine back pressure set point x1, such as corrections that account for ambient temperature and pressure. A difference d is then taken between the correction value c and the engine back pressure set point x1 at difference calculation step 128.

Referring now to FIG. 3 from FIG. 2, the method 100 continues by determining an open loop control value l at loop value step 132 using the engine speed s previously obtained. A calculated factor f is determined at factor step 134, which is used with the difference d to determine a proportional gain p at gain step 136. One way of obtaining the proportional gain p is by multiplying the difference d and the calculated factor f.

An integral gain i is determined at integral step 138, such as by taking the integration of the difference d. An exhaust valve set point v is determined at valve set point step 140 using the proportional gain p, the integral gain i, and the open loop control value l. It is possible that other implementations can be used to obtain any of the above variables.

When the exhaust valve set point v is obtained at step 140, the exhaust valve 28 is actuated to close, completely or partially, at valve actuation step 142, heating the exhaust gas in the fluid passageway 20. Actuation of the exhaust valve 28 causes the exhaust gas temperature to increase, which heats the DOC 23 and initiates regeneration at the DPF 24. When the DPF 24 is regenerated, the exhaust valve 28 is opened and the method ends at end step 144. From the end step 144, the method restarts to the beginning step 102 shown in FIG. 2. 

1) A method of operating an exhaust valve to heat a diesel oxidation catalyst and initiate regeneration of a diesel particulate filter on an exhaust aftertreatment system associated with an engine, the method comprising the steps of: determining whether the diesel particulate filter is being cleaned; determining the speed of the engine; determining the quantity of fuel injected to the engine; determining an engine back pressure set point based on whether the engine is fueling, wherein when the engine is fueling, the engine back pressure set point is based on the quantity of fuel and the speed of the engine, and wherein when the engine is not fueling, the engine back pressure set point is based on whether there is an other request for actuation of the exhaust valve; determining a current engine back pressure; determining an exhaust valve set point based on the engine back pressure set point and the current engine back pressure; and actuating the exhaust valve in response to the exhaust valve set point to at least partially obstruct the flow of exhaust gas through a fluid passageway of the exhaust aftertreatment system, wherein the exhaust gas is heated in the fluid passageway and initiates regeneration of the diesel particulate filter. 2) The method of claim 1 wherein when there is no other request, the back pressure set point is determined by a braking torque of the engine and the speed of the engine, and when there is an other request, the back pressure set point is determined by the other request. 3) The method of claim 1 wherein the step of determining whether the diesel particulate filter is being cleaned is based on output from a sensor that senses at least one of a backpressure in the aftertreatment system and a temperature in the aftertreatment system. 4) The method of claim 1 further comprising the steps of determining the acceleration of the engine, wherein when the acceleration is greater than zero, the quantity of fuel is determined. 5) The method of claim 1 further comprising the steps of determining the acceleration of the engine, and subsequently determining whether there is the other request for the exhaust valve when the acceleration is not greater than zero. 6) The method of claim 1 further comprising the step of determining a correction value to the engine back pressure set point based on the ambient pressure and temperature. 7) The method of claim 6 further comprising the steps of determining a difference between the correction value and the current engine back pressure, and setting the exhaust valve set point based on the difference. 8) The method of claim 7 further comprising the steps of determining a calculated factor of the engine, and determining a proportional gain using the difference and the calculated factor. 9) The method of claim 8 further comprising the step of setting the exhaust valve set point based on the proportional gain. 10) The method of claim 8 further comprising the step of determining an integral gain using the difference; and setting the exhaust valve set point based on the integral gain. 11) The method of claim 10 further comprises taking an integration of the difference to determine the integral gain. 12) The method of claim 1 further comprising the steps of determining an open loop control value using the engine speed, and determining the exhaust value set point based on the open loop control value. 